Wood laminate material and method for manufacturing same

ABSTRACT

Provided is a strand board with improved strength and water resistance. Reduction in productivity is prevented and characteristics of the strand board can be varied as desired while achieving certain strength and water resistance of the strand board. A strand board B is formed by stacking and laminating five strand layers 1 each formed by a large number of strands 5. The strand board B has substantially constant density distribution in the lamination direction of the strand layers 1. Three of the five strand layers 1 of the strand board B are high-density strand layers 1a having a higher density than the other strand layers 1, and the other strand layers 1 are low-density strand layers 1b.

This is a divisional under 35 USC § 120 of U.S. application Ser. No.16/088,904, filed Sep. 27, 2018, which is a national stage under 35 USC§ 371 of International Application No. PCT/JP2017/033872, filed Sep. 20,2017, which claims priority under 35 USC § 119 to Japanese PatentApplication Nos. 2016-194762, filed Sep. 30, 2016 and 2017-063447, filedMar. 20, 2017. The disclosure of each of these applications isincorporated herein in its entirety.

TECHNICAL FIELD

The present invention relates to wood laminate materials that are formedby stacking and laminating multiple woodbased material layers eachformed by a woodbased material or woodbased materials, and methods formanufacturing the same.

BACKGROUND ART

Today there are less and less tropical hardwood species includingbroadleaf tress such as apitong and keruing, and it is difficult toobtain high-quality veneer at low cost. Degradation in quality ofplywood using tropical hardwood species has therefore become a bigproblem. Wood fiberboards such as oriented strand boards (OSBs) areincreasingly used as a substitute material for plywood. However, OSBswith common densities do not provide sufficient strength.

Conventionally, Patent Document 1, for example, discloses a large OSBplate having a density of at most 700 kg/m³, a length of at least 7 m,and a flexural modulus of at least 7000 N/mm² in the primary loaddirection.

Patent Document 2 discloses a technique of using a strand material,which is formed by orienting and stacking woodbased material pieces andcompressing and heating the stack, for joists, foundations, etc.

CITATION LIST Patent Document

-   PATENT DOCUMENT 1: Japanese Patent No. 4307992-   PATENT DOCUMENT 2: Japanese Patent No. 4227864

SUMMARY OF THE INVENTION Technical Problem

In the OSB plate of Patent Document 1, a press pressure higher thancommon pressures is required to form a board. This OSB plate thereforecannot be formed without using a special press machine.

The inventors found that a board formed at a press pressure higher thancommon pressures with a special press machine as described above hasuneven density distribution in the thickness direction of the boards. Aboard having uneven density distribution tends to be weak in itslow-density portion. Moreover, the low-density portion of the board ismore water absorbent and thus has lower water resistance as compared toa high-density portion of the board. With such uneven densitydistribution, strength and water resistance are governed by thelow-density portion, and sufficient strength and water resistance cannotbe obtained.

High strength and high water resistance can be achieved by using layerswith a high density as all of woodbased material layers of a woodlaminate material that is a laminate of woodbased materials such asstrands.

In this case, however, it takes a lot of time and effort to increase thedensity of all of the multiple woodbased material layers of the woodlaminate material, and reduction in productivity is thereforeunavoidable. Moreover, since all of the woodbased material layers have ahigh density, characteristics as the wood laminate material are alwaysthe same, and it is difficult to vary characteristics of the woodlaminate material for various applications.

It is an object of the present invention to allow a wood laminatematerial, which is a laminate of multiple woodbased materials, to havehigh strength and high water resistance by adjusting densitydistribution in the lamination direction, namely the direction in whichthe woodbased materials are laminated. It is another object of thepresent invention to prevent reduction in productivity for manufacturingwood laminate materials and make it possible to vary characteristics ofthe wood laminate materials while achieving a certain level of strengthand water resistance of the wood laminate materials.

Solution to the Problem

In order to achieve the above objects, in the present invention, a woodlaminate material is formed so as to have substantially constant densitydistribution in the lamination direction, thereby improving strength andwater resistance of the wood laminate material.

Specifically, in the present invention, a wood laminate material formedby stacking and laminating multiple woodbased material layers eachformed by laminated woodbased materials that are laminated multiple cutpieces or a woodbased material that is a veneer is characterized byhaving substantially constant density distribution in a laminationdirection of the woodbased material layers.

According to this configuration, the wood laminate material hassubstantially constant density distribution in the lamination direction.As described above, if the wood laminate material has uneven densitydistribution in the lamination direction, strength and water resistanceof the wood laminate material are governed by a low-density portion.However, the wood laminate material according to the present inventiondoes not have such a problem. A wood laminate material with highstrength and high water resistance is thus implemented.

In the above configuration, the woodbased material may have a density of300 kg/m³ or more and 1100 kg/m³ or less, and preferably 300 kg/m³ ormore and 800 kg/m³.

Since the woodbased material has a density of 300 kg/m³ or more, thethickness of a stack of woodbased material layers (the thickness of thestack before being laminated) required to form a wood laminate materialwith the same density and strength can be reduced. Since the thicknessof the stack can be reduced, workability of processes associated withlamination (e.g., a stacking process and a forming process) is improved.Moreover, a pressure for lamination which is required to form a woodlaminate material with the same density and strength can be reduced.

The multiple woodbased material layers may be composed so that athickness of the woodbased material layer gradually increases from themiddle woodbased material layer in the lamination direction of the woodlaminate material to the top and bottom woodbased material layers.

The outer layers that are more likely to be subjected to load and impactand are more susceptible to humidity etc. thus have a larger thicknessthan the inner layer(s). This allows the wood laminate layer to haveimproved performance regarding influences from the external environment.

In the present invention, not all of the woodbased material layers ofthe wood laminate material have a high density, but only a part of thewoodbased material layers has a high density. High strength, high waterresistance, etc. of the wood laminate material are thus implemented bythe woodbased material layer with a high density.

Specifically, a wood laminate material formed by stacking and laminatingmultiple woodbased material layers each formed by laminated woodbasedmaterials that are laminated multiple cut pieces or a woodbased materialthat is a veneer is characterized in that the multiple woodbasedmaterial layers include at least one high-density woodbased materiallayer, the remainder of the multiple woodbased material layers is alow-density woodbased material layer, and the high-density woodbasedmaterial layer has a higher density than the low-density woodbasedmaterial layer. As used herein, the “density of the woodbased materiallayer” refers to the density of a mat of cut pieces in the case wherethe woodbased materials are cut pieces, and refers to the density of aveneer if the woodbased material is a veneer.

In this configuration, at least one of the multiple woodbased materiallayers is a high-density woodbased material layer, and the remainder ofthe woodbased material layers is a low-density woodbased material layer.High strength and high water resistance of the wood laminate materialare thus implemented by the high-density woodbased material layer.

In the case where the density of the woodbased material layer isincreased, the density of the woodbased material need be increased onlyin the woodbased material layer required to have a high density, and itis not necessary to increase the density of the woodbased material inall the woodbased material layers. Press time with a press machine istherefore reduced accordingly and the pressure to be used is alsoreduced. This improves productivity and reduces or eliminates the riskof delamination when forming the wood laminate material.

Moreover, since at least one of the woodbased material layers is ahigh-density woodbased material layer, the layer(s) to be used as ahigh-density woodbased material layer can be selected as necessary fromthe multiple woodbased material layers. Characteristics of the woodlaminate material can thus be varied as desired by changing theposition(s) of the high-density woodbased material layer(s).

In the above configuration, the woodbased material layers located atboth ends in the lamination direction of the woodbased material layersmay be the high-density woodbased material layers.

In this case, the woodbased material layers located at both ends in thelamination direction are the high-density woodbased material layers andhave a higher density than the woodbased material layer(s) located inthe remaining part. This improves flexural strength of the wood laminatematerial and also improves water resistance of the top and bottom partsof the wood laminate material.

The woodbased material layer located in an intermediate part in thelamination direction of the woodbased material layers may be thehigh-density woodbased material layer.

In this case, as opposed to the case described above, the woodbasedmaterial layer located in the intermediate part in the laminationdirection of the woodbased material layers is the high-density woodbasedmaterial layer and has a higher density than the woodbased materiallayers located in the remaining part (at both ends in the laminationdirection of the woodbased material layers). The density in theintermediate part is therefore increased. This allows the wood laminatematerial to have uniform density distribution in the laminationdirection. Moreover, since the wood laminate material has thehigh-density woodbased material layer in its intermediate part in thethickness direction and the top and bottom parts of the wood laminatematerial have a low density, the risk of delamination when forming thewood laminate material is effectively reduced or eliminated andproductivity is improved.

The woodbased material layer located in a part other than the ends and amiddle part in the lamination direction of the woodbased material layersmay be the high-density woodbased material layer.

In this configuration, the woodbased material layer located in the partother than the ends and the middle part in the lamination direction ofthe woodbased material layers is the high-density woodbased materiallayer, and the woodbased material layers located at the ends and in themiddle part in the lamination direction have a low density. The pressureto be used to form the wood laminate material is thus reduced by thelow-density woodbased material layers in the top and bottom parts of thewood laminate material, and nail pull resistance (force) of the woodlaminate material is increased by the high-density woodbased materiallayer.

Fibers of the woodbased materials may extend in the same direction ineach woodbased material layer, and the fibers of the woodbased materialsin adjoining ones of the woodbased material layers may extend indirections crossing or parallel to each other.

As used herein, the expressions “fibers extend in the same direction”and “fibers extend in directions parallel to each other” are not limitedto the case where the fibers of all the woodbased materials are orientedin the same direction, but define a concept including the case where thefibers of a part of the woodbased materials are tilted to some extent.The fibers of a part of the woodbased materials may be tilted by, e.g.,about 20° with respect to a predetermined reference direction.Similarly, the expression “fibers extend in directions crossing eachother” is not limited to the case where the fibers are oriented indirections perpendicular to each other. The fibers of a part of thewoodbased materials may be tilted by, e.g., about 20° with respect to adirection perpendicular to the reference direction.

According to this configuration, in the case where the fibers of thewoodbased materials in adjoining ones of the woodbased material layersextend in directions crossing each other, the wood laminate material hashigh strength against forces acting in various directions, as comparedto the case where the fibers extend in the same direction in all of thewoodbased material layers. Especially, the larger the number ofwoodbased material layers is, the more significant the difference instrength due to the difference in fiber direction between the woodbasedmaterial layers is. In the case where the fibers are oriented in thesame direction along the entire thickness in the lamination direction ofthe wood laminate material, the strength may vary depending on thedirection in which a force is applied. However, this problem does notoccur in the case where the fibers of the woodbased materials inadjoining ones of the woodbased material layers extend in directionscrossing each other.

On the other hand, in the case where the fibers of the woodbasedmaterials in adjoining ones of the woodbased material layers extend indirections parallel to each other, namely in the case where the fiberdirections of the woodbased materials are the same along the entirethickness in the lamination direction of the wood laminate material, thewood laminate material has high strength against a force acting in aspecific direction.

Of the multiple woodbased material layers, the fibers of the woodbasedmaterials in the top and bottom woodbased material layers may extend inthe same direction.

Performance such as load resistance and impact resistance in the toppart of the wood laminate material is therefore about the same as thatin the bottom part of the wood laminate material. That is, thisconfiguration allows the wood laminate material to have similarperformance in its top and bottom parts. This is advantageous in thatthe user can use the wood laminate material without having to worryabout which side is the top and which side is the bottom.

The number of woodbased material layers may be odd. In this case, thewood laminate material is a laminate of the odd number of woodbasedmaterial layers. This configuration allows the wood laminate material tohave similar performance in its top and bottom parts, as in the casedescribed above.

The multiple woodbased material layers may be laminated so that overalldensity distribution provided by the multiple woodbased material layersis plane symmetric with respect to a center in the lamination direction.Since the overall density distribution provided by the multiplewoodbased material layers is plane symmetric with respect to the centerin the lamination direction, the wood laminate material has similarperformance in its top and bottom parts. The user can therefore use thewood laminate material without having to know which side is the top andwhich side is the bottom.

The woodbased materials may be strands that are cut pieces. Thisimplements a strand material having high strength and high waterresistance or a strand material having high productivity and variedcharacteristics.

A method for manufacturing a wood laminate material is characterized byincluding: a stacking step of stacking multiple woodbased materials,which are cut pieces or veneers, to form multiple woodbased materiallayers so that at least one of the multiple woodbased material layers isformed by a high-density woodbased material or high-density woodbasedmaterials having a relatively higher density than the remainder of thewoodbased material layers; and a forming step of compressing orcompacting the multiple woodbased material layers formed in the stackingstep.

Since the woodbased material layers include a layer formed by thehigh-density woodbased material or high-density woodbased materialshaving a relatively higher density than the remainder of the woodbasedmaterial layers, density distribution in the lamination direction afterthe forming step can be adjusted, whereby a wood laminate material withdesired characteristics can be produced. For example, densitydistribution in the lamination direction of the wood laminate materialcan be made substantially constant by inserting the woodbased materiallayer formed by the high-density woodbased material or high-densitywoodbased materials at an optimal position.

Advantages of the Invention

As described above, according to the present invention, densitydistribution in the lamination direction of the wood laminate material,which is formed by stacking and laminating multiple woodbased materiallayers each formed by cut pieces or veneer, is adjusted so that the woodlaminate material has substantially constant density distribution in thelamination direction. High strength and high water resistance cantherefore be achieved. Moreover, the density distribution in thelamination direction is varied so that at least one of the multiplewoodbased material layers is a high-density woodbased material layerhaving a higher density than the remainder of the woodbased materiallayers. Accordingly, only the woodbased material layer required to havehigh strength and high water resistance has a high density, andproductivity is improved. Moreover, characteristics of the wood laminatematerial can be varied as desired by changing the layer that is to be ahigh-density woodbased material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a multi-layered structure of astrand board according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view of a first example of a strandboard according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a laminate of strand layersin the first example of the strand board according to the secondembodiment.

FIG. 4 is a sectional view corresponding to FIG. 3, showing a secondexample of the strand board according to the second embodiment.

FIG. 5 is a sectional view corresponding to FIG. 3, showing a thirdexample of the strand board according to the second embodiment.

FIG. 6 is a sectional view corresponding to FIG. 3, showing a fourthexample of the strand board according to the second embodiment.

FIG. 7 is a sectional view corresponding to FIG. 3, showing a fifthexample of the strand board according to the second embodiment.

FIG. 8 is a sectional view corresponding to FIG. 3, showing a sixthexample of the strand board according to the second embodiment.

FIG. 9 is a table illustrating specific configurations of the first tosixth examples of the strand board according to the second embodiment.

FIG. 10 is a sectional image of a strand board of Example 1 of the firstembodiment.

FIG. 11 is a table showing the test results of Examples 1, 2 andComparative Examples 1, 2.

FIG. 12 is a graph showing density distribution in the strand board ofExample 1 according to the first embodiment, in which the uniformshort-dashed line represents an average density of the woodbasedmaterial layers in the thickness direction (lamination direction) andthe long-dash short-dash line represents a constant density value forreference.

FIG. 13 is a graph showing density distribution in a strand board ofComparative Example 1 as compared to the first embodiment, in which theuniform short-dashed line represents an average density of the woodbasedmaterial layers in the thickness direction (lamination direction) andthe long-dash short-dash line represents a constant density value forreference.

FIG. 14 is a table showing the results of a bending test for Examples 1,2 and Comparative Example 1 of the second embodiment, along with theirother physical properties.

FIG. 15 is a graph showing density distribution in the thicknessdirection (lamination direction) of Examples 1, 2 and ComparativeExample 1 according to the second embodiment.

FIG. 16 is a table showing the results of a bending test and a boilingtest for Example 3 and Comparative Example 2, along with their otherphysical properties.

FIG. 17 is a graph showing density distribution in the thicknessdirection (lamination direction) of Example 3 and Comparative Example 2according to the second embodiment.

FIG. 18 is a table showing the results of a bending test and a boilingtest for Example 4 and Comparative Example 3, along with their otherphysical properties.

FIG. 19 is a table showing the result of a nail pull test for Example 4and Comparative Example 4, along with their other physical properties.

FIG. 20 is a graph showing density distribution in the thicknessdirection (lamination direction) of Example 4 and Comparative Example 3according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings. The following descriptionof the preferred embodiments is merely exemplary in nature and is notintended in any way to limit the invention, its applications or uses.Specific numerical values in the embodiments are shown merely by way ofexample in order to facilitate understanding of the invention and arenot intended to limit the scope of the invention and materials of theinvention.

First Embodiment

FIG. 1 schematically shows a strand board B as a wood laminate materialaccording to a first embodiment of the present invention.

As shown in FIG. 1, the strand board B has an odd number of (in FIG. 1,five) strand layers 1, 1, . . . as woodbased material layers, and all ofthe strand layers 1, 1, . . . have the same thickness. That is, FIG. 1shows an example in which, with the upper side in FIG. 1 being the topand the lower side being the bottom, the thickness w1 of the top andbottom strand layers 1, 1 is the same as the thicknesses w2, w3, w2 ofthe three intermediate strand layers 1, 1, . . . . The strand board Bneed not necessarily have an odd number of strand layers 1. The strandboard B may have an even number of strand layers 1. The number of strandlayers 1 is not limited to five. The number of strand layers 1 may befour or less or six or more.

Each strand layer 1 is a mat made of laminated multiple strands 5, 5, .. . (woodbased materials) that are cut pieces of wood etc. Multiple matsof strands 5, 5, . . . are stacked together to form multiple strandlayers 1, 1, . . . .

For example, the strands 5 are strands or flakes that are about 150 to200 millimeters long in the fiber direction, about 15 to 25 millimeterswide, and about 0.3 to 2 millimeters thick.

Wood species that are used for the strands 5 are not particularlylimited. For example, tropical wood species or broadleaf trees may beused, or other wood species may be used. Specific examples include Cedar(Cryptomeria japonica), Cypress (Chamaecyparis), sort of firs such asDouglas fir (Pseudotsuga menziesii), Acacia (Acacia spp.), Aspen(Populus spp.), Poplar (Populus spp.), Pine (Pinus spp.) (Hard pine(Pinus spp.), Soft pine (Pinus spp.), Radiata pine (Pinus radiata),etc.), Birch (Betula spp.), and Rubber tree (Rubber wood (Heveabrasiliensis)). However, the wood species that are used for the strands5 are not limited to these, and various other wood species may be used.Examples of the various other wood species include: Japanese woodspecies such as Sawara cypress (Chamaecyparis pisifera), Japaneseelkhorn cypress (Thujopsis dolabrata), Japanese nutmeg-yew (Torreyanucifera), Southern Japanese hemlock (Tsuga sieboldii), Podocarp(Podocarpus macrophyllus), Pinus spp., Princess tree (Paulowniatomentosa), Maple (Acer spp.), Birch (Betula spp.) (Japanese white birch(Betula platyphylla)), Chinquapin (Castanopsis spp.), Japanese beech(Fagus spp.), Live oak (Quercus spp.), Abies firma, Sawtooth oak(Quercus acutissima), Oak (Quercus spp.), Camphor tree (Cinnamomumcamphora), and Japanese zelkova (Zelkova serrata); North American woodspecies such as Port Orford cedar (Chamaecyparis lawsoniana), Yellowcedar (Callitropsis nootkatensis), Western redcedar (Thuja plicata),Grand fir (A. grandis), Noble fir (A. procera), White fir (A. concolor),Spruce (Picea spp.), Western hemlock (Tsuga heterophylla), and Scotspine (Pinus sylvestris); tropical hardwood species such as Agathis(Agathis spp.), Terminalia (Terminalia spp.), Lauan (Shorea spp.),Meranti (Shorea sect.), Sengon laut (A. falcataria), Jongkong(Dactylocladus stenostachys), Kamerere (Eucalyptus deglupta), Kalampayan(Anthocephalus chinensis), Amberoi (Pterocymbium beccarii), Yemane(Gmelina arborea), Teak (Tectona grandis), and Apitong (Dipterocarpusspp.); and other foreign wood species such as Balsa (Ochromapyramidale), Cedro (Cedrela odorata), Mahogany (Swietenia spp.),Lignum-vitae (Guaiacum spp.), Acacia mangium, Aleppo pine (Pinushalepensis), Bamboo, Sorghum (Sorghum nervosum Bess.), and Kamerere(Eucalyptus deglupta). Any material can be used.

Regarding physical properties of the strands 5, the strands 5 preferablyhave a density of about 300 to 800 kg/m³, more preferably 430 to 700kg/m³. If the density is less than 300 kg/m³, a multi-layered mat with alarger thickness is required to form a strand board B of the samedensity and strength, and a higher pressure need be used for hotpressing in a press process described later.

The strands 5 may have a density higher than 800 kg/m³, but it isdifficult to obtain such strands 5. Namely, if strands 5 having adensity higher than 800 kg/m³ can be easily obtained, the upper limit ofthe density is not limited to 800 kg/m³ and may be higher than 800kg/m³.

The moisture content of each strand 5 is preferably about 2 to 20%, morepreferably 2 to 8%. If the moisture content is less than 2%, it takesmore time to soften the strands 5 in the hot pressing of the pressprocess. Namely, the press time is increased, which may cause reductionin strength.

If the moisture content of the strands 5 is higher than 20%, it takesmore time to heat and compress the strands 5 in the hot pressing, andthe strands 5 tend to be blown. Moreover, curing of an adhesive isinhibited, which may cause reduction in strength.

In each strand layer 1, the strands 5, 5, . . . are oriented such thatthe fiber direction (longitudinal direction of the strands 5), which isthe direction in which fibers (not shown) of the strands 5, 5, . . .extend, is a predetermined direction. As also shown in FIG. 1, thefibers of the strands 5, 5, . . . in each strand layer 1 need notnecessarily extend in exactly the same direction. In other words, thefiber directions of the oriented strands 5, 5, . . . do not have to beparallel to each other. Namely, the fiber directions of a part of thestrands 5, 5, . . . may be tilted to some extent (e.g., by about 20°)with respect to a predetermined reference direction.

The multiple strand layers 1, 1, . . . are stacked and laminated suchthat the fibers of the strands 5, 5, . . . in adjoining ones of thestrand layers 1 extend in directions perpendicular to each other. Thatis, in FIG. 1, the fiber direction of the strands 5, 5, . . . in the topstrand layer 1 (uppermost layer in FIG. 1) is the same as that of thestrands 5, 5, . . . in the bottom strand layer 1 (lowermost layer inFIG. 1).

The first embodiment is characterized in that the strand board B hassubstantially constant density distribution in the lamination directionof the strand layers 1 (the thickness direction of the strand board B),namely the direction in which the strand layers 1 are laminated.Specifically, the multiple strand layers 1, 1, . . . are laminated sothat overall density distribution provided by the multiple strand layers1, 1, . . . is plane symmetric with respect to the center in thelamination direction of the strand board B.

Next, a method for manufacturing a strand board B according to the firstembodiment will be described. This manufacturing method includes astrand producing process, a strand pretreatment process, an adhesivecoating process, a stacking process (mat forming process), and a pressprocess.

(Strand Producing Process)

In the method for manufacturing a strand board B, the strand producingprocess is first performed in which a large number of strands 5, 5, . .. (cut pieces of wood etc.) are produced. In this process, green woodsuch as logs or thinnings is cut with, e.g., a cutting machine toproduce strands 5, 5, . . . . The strands 5, 5, . . . may be producedfrom wood scraps, wood wastes, etc. that are generated at constructionsites etc. or may be produced from waste wood pallets.

(Strand Pretreatment Process)

After the strand producing process, it is preferable that a large numberof strands 5, 5, . . . produced be subjected to at least one of variousstrand pretreatment processes described below. This pretreatment isperformed in order to allow low-pressure pressing using a pressure aslow as, e.g., about 4 N/mm² to be performed in the later press process.At least one of a physical treatment method, a high-frequency treatmentmethod, a high-temperature high-pressure treatment method, a high-waterpressure treatment method, a repeated deaeration and dehydrationtreatment method, and a chemical treatment method is used.

The physical treatment method is a method in which the strands 5 arephysically compressed. Examples of the physical treatment method includeroll pressing, beating, and flat press pressing. The roll pressing is alinear compression method in which, although not shown in the figures, alarge number of strands 5, 5, . . . (woodbased materials) are placed ina heat roll press machine such that the strands 5, 5, . . . evenly dropthereon, and the strands 5, 5, . . . are then compressed with heat. Forexample, this roll pressing is performed under the following conditions:heating temperature: room temperature to 200° C.; clearance between heatrolls: about 0.1 to 0.4 mm; feed rate: about 50 m/min; and compressionratio: about 20 to 60%. The strands 5 are thus compressed without beingsmashed, whereby high-density strands 5 are produced.

The beating is a point compression method in which, as in metal forging,strands 5 are compressed and deformed by hitting with multiplecontinuously installed spring hammers etc. As in the roll pressing, thestrands 5 are thus compressed without being smashed, wherebyhigh-density strands 5 are produced.

The flat press pressing is a surface compression method in which strands5, 5, . . . (woodbased materials) are placed in a flat heat pressmachine and compressed with heat. For example, the flat press pressingis performed at a temperature of 120° C. and a pressure of about 4 N/mm²for about five minutes. In the flat press pressing as well, the strands5 are compressed without being smashed, whereby high-density strands 5are produced.

The high-frequency treatment method is a method in which strands 5 asdielectrics (nonconductors) are irradiated with high-frequencyelectromagnetic waves (high-frequency waves) between electrodes etc. andthus dielectrically heated from the inside and softened. This methodallows low-pressure pressing using a low pressure to be performed in thelater press process without increasing the density of the strands 5 asin the above physical treatment method.

The high-temperature high-pressure treatment method is a method in whichstrands 5 are placed in a pressure vessel where the strands 5 aresubjected to high temperature and high pressure so that cell walls ofthe strands 5 (woodbased materials) are damaged and the strands 5 aresoftened. For example, this method is performed at a temperature of 180°C. and a pressure of about 10 Bar for about two minutes. This methodalso allows low-pressure pressing using a low pressure to be performedin the later press process without increasing the density of the strands5 as in the above physical treatment method.

The high-water pressure treatment method is a method in which strands 5are uniformly formed within a mesh material such as metal wire mesh andthe surfaces of the strands 5 are finely scratched by high-pressurewater of, e.g., about 200 MPa through the mesh material. This producesfine fractures in the strands 5. The softened strands 5 are thusobtained.

The repeated deaeration and dehydration treatment method is a method inwhich strands 5 are first saturated with water and then placed in abatch type of vessel, and with the vessel being evacuated to vacuum,moisture is removed from the strands 5 to facilitate damage to cellwalls of the strands 5 (woodbased materials) and thus soften the strands5. This method also allows low-pressure pressing using a low pressure tobe performed in the later press process without increasing the densityof the strands 5 as in the above physical treatment method.

The chemical treatment method is a method in which, for example, sodiumhydroxide etc. is added to strands 5 for alkaline treatment tofacilitate plasticization of the strands 5 themselves and thus softenthe strands 5. This method also allows low-pressure pressing using a lowpressure to be performed in the later press process without increasingthe density of the strands 5 as in the above physical treatment method.

In the high-frequency treatment method, the high-temperaturehigh-pressure treatment method, the high water pressure treatmentmethod, the repeated deaeration and dehydration treatment method, andthe chemical treatment method, the state of the strands 5 after thetreatment is maintained by drying the strands 5 as necessary after thetreatment.

(Adhesive Coating Process)

After a large number of strands 5, 5, . . . are thus produced, theadhesive coating process is performed in which the strands 5, 5, . . .are coated with an adhesive. For example, the adhesive may be anisocyanate adhesive or may be an amine adhesive such as a phenol resin,urea resin, or melamine resin.

(Stacking Process)

Thereafter, the stacking process (mat forming process) is performed inwhich a large number of strands 5, 5, . . . are oriented and stacked toform strand mats and the strand mats are stacked in multiple layers toform a multi-layered mat.

Specifically, with a mat forming machine etc., a large number of strands5, 5, . . . coated with the adhesive are oriented such that fibersextend in a predetermined reference direction, and are stacked to athickness of, e.g., about 7 to 12 mm to form a strand mat with a certainthickness. The thickness of the strand mat is not limited to the abovevalues. The thickness of the strand mat may be less than 7 mm or morethan 12 mm.

After the strand mat with a certain thickness is thus formed, strands 5,5, . . . oriented such that the fiber direction of the strands 5, 5, . .. is, e.g., perpendicular to that of the strands 5, 5, . . . in thestrand mat are stacked on top of the strand mat to form another strandmat with a certain thickness.

Subsequently, an additional strand mat is repeatedly stacked in asimilar manner until the stack has a desired number of layers (e.g.,five layers). At this time, the strand mats are stacked so that thefiber directions of the strands 5, 5, . . . in adjoining ones of thestrand mats are perpendicular to each other. A multi-layered mat isformed in this manner. As shown in FIG. 1, in the case of the strandboard B having the five strand layers 1, 1, . . . , the thickness of thefive-layered mat is, e.g., about 35 to 60 mm.

The number of strand mats in the multi-layered mat is determined basedon the number of layers in the strand board B. Accordingly, the numberof strand mats in the multi-layered mat may be four or less or six ormore.

The density of the strands 5, 5, . . . of the strand layer 1 may beeither about the same or different between or among the multiple strandlayers 1, 1, . . . .

(Press Process)

After the multi-layered mat is thus formed by stacking multiple strandmats, hot pressing is performed at a predetermined pressure andtemperature with a hot press machine to compress or compact themulti-layered mat. This hot pressing is performed at a pressure of,e.g., 2 to 4 N/mm² for, e.g., about 10 to 20 minutes. The press timevaries depending on the thickness of the strand board B (finishedproduct). Accordingly, in some cases, it may take less than 10 minutesto complete the hot pressing, and in other cases, it may take 20 minutesor more to complete the hot pressing. Pre-heat treatment with a heatermay be performed before the hot pressing with the hot press machine.

A strand board B having a density of 750 to 950 kg/m³ and flexuralstrength of 80 to 150 N/mm² is thus formed as a laminate by theseprocesses.

In the first embodiment, the pressure for the hot pressing in the pressprocess is as low as 2 to 4 N/mm². A high density, high strength strandboard B can thus be produced without using a special high pressure pressmachine.

In the strand board B, the fiber direction of the strands 5, 5, . . . inthe top strand layer 1 of the strand board B is the same as that of thestrands 5, 5, . . . in the bottom strand layer 1 of the strand board B.Performance such as load resistance and impact resistance in the toppart of the strand board B is therefore about the same as that in thebottom part of the strand board B. That is, this configuration allowsthe strand board B to have similar performance in its top and bottomparts. This is advantageous in that the user can use the strand board Bwithout having to worry about which side is the top and which side isthe bottom.

The multiple strand layers 1, 1, . . . have about the same thickness.This allows the strand board B to have uniform board performance such asstrength properties and water resistance properties in the thicknessdirection.

Density distribution in the thickness direction of the strand board Bformed by the strand layers 1, 1, . . . is plane symmetric. This allowsthe strand board B to have similar performance in its top and bottomparts. The user can therefore use the strand board B without having toknow (worry about) which side is the top and which side is the bottom.

In the case where the number of strand layers 1, 1, . . . is odd, thestrand board B has similar performance in its top and bottom parts, asdescribed above.

As described above, it is preferable that the strands 5, 5, . . .produced in the strand producing process have a density of 430 to 700kg/m³ and a moisture content of 2 to 20%. However, the strands 5, 5, . .. produced in the strand producing process can be used even if theirproperties are out of these preferred ranges.

Specifically, the strands 5, 5, . . . having desired properties may beseparated from strands cut (or sliced) from logs by a screening machineetc., and the strands 5, 5, . . . thus separated may be subjected to thesubsequent processes, namely the strand producing process, the strandpretreatment process, the adhesive coating process, the stacking process(mat forming process), and the press process.

The substantial moisture content and density of the strands 5, 5, . . .may be adjusted by changing, e.g., the composition, the coating method,etc. of the adhesive that is used in the adhesive coating process asdesired. A predetermined pressing process may be performed, e.g., duringor before the hot pressing in the press process. Specifically, apressing process (including a compressed process) may be divided into inmultiple stages to adjust the substantial moisture content of thestrands 5, 5, . . . or increase the substantial density of the strands5, 5, . . . for the hot pressing.

Second Embodiment

FIGS. 2 to 8 shows a second embodiment of the present invention (thesame portions as those in FIG. 1 are denoted with the same referencecharacters and detailed description thereof will omitted). FIGS. 2 to 8show examples of a strand board B that is a wood laminate materialaccording to the second embodiment. FIGS. 2 and 3 show a first exampleof the strand board B. FIG. 4 shows a second example, FIG. 5 shows athird example, FIG. 6 shows a fourth example, FIG. 7 shows a fifthexample, and FIG. 8 shows a sixth example.

In each of the first to sixth examples, the strand board B includesstrand layers 1, 1, . . . as multiple (an odd number of) woodbasedmaterial layers. Each strand layer 1 is made of a mat of a large numberof strands 5, 5, . . . (woodbased materials) that are cut pieces.Multiple mats of strands 5, 5, . . . are stacked together to formmultiple strand layers 1, 1, . . . .

In the second embodiment, the upper side in FIGS. 3 to 8 is the top ofthe strand board B and the lower side is the bottom thereof, and thestrand layers 1, 1, . . . are sequentially numbered from top to bottomas the first strand layer 1, the second strand layer 1, the third strandlayer 1, . . . . The strand layers 1, 1, . . . are thus marked withcircled numbers in the FIGS. 3 to 8.

In the second embodiment, the strands 5 preferably have a density ofabout 300 to 1100 kg/m³. If the density is less than 300 kg/m³, amulti-layered mat with a larger thickness is required to formhigh-density strand layers 1 a, and a higher pressure need be used forhot pressing in a press process.

The strands 5 may have a density higher than 1100 kg/m³, but it isdifficult to obtain such strands 5. Namely, if strands 5 having adensity higher than 1100 kg/m³ can be easily obtained, the upper limitof the density is not limited to 1100 kg/m³ and may be higher than 1100kg/m³.

In the second embodiment as well, the strands 5, 5, . . . in each strandlayer 1 are oriented such that the fibers of the strands 5, 5, . . .extend in a predetermined direction. As also shown in FIG. 2, the fibersof the strands 5, 5, . . . in each strand layer 1 need not necessarilyextend in the same direction. Namely, the fiber directions of theoriented strands 5, 5, . . . in each strand layer 1 do not have to beparallel to each other. In other words, the fibers of a part of thestrands 5, 5, . . . in each strand layer 1 may be tilted to some extentwith respect to a predetermined reference direction. For example, a partof the strands 5, 5, . . . in each strand layer 1 may be oriented so asto be tilted by about 20° with respect to the reference direction.

The second embodiment is characterized in that, unlike in the firstembodiment, at least one of the odd number of strand layers 1, 1, . . .in the strand board B is a high-density strand layer 1 a having adensity higher than the remaining strand layers 1 b, and the remainingstrand layers 1 b are low-density strand layers. The “density of thestrand layer” as used in the second embodiment does not refer to thedensity of the strands 5 but refers to the density of the strand layer 1itself made of a mat of the strands 5.

Each example of the strand board B will be specifically described indetail. In FIGS. 3 to 8, the layers shaded with dense dots represent thehigh-density strand layers 1 a and the layers shaded with sparse dotsrepresent the low-density strand layers 1 b.

First Example

FIGS. 2 and 3 show the first example of the strand board B according tothe second embodiment. This strand board B has five strand layers,namely first to fifth strand layers 1, 1, . . . . These strand layers 1,1, . . . are stacked and laminated such that the fibers of the strands5, 5 in adjoining ones of the strand layers 1 extend in directionsperpendicular to each other. The fiber direction of the strands 5, 5 inthe first strand layer 1 located at the top of the strand board B,namely in the uppermost strand layer 1 in FIG. 3, is the same as that ofthe strands 5, 5 in the fifth strand layer 1 located at the bottom ofthe strand board B, namely in the lowermost strand layer 1 in FIG. 3.

Two of the five strand layers 1, 1, . . . are high-density strand layers1 a having a density higher than the other three strand layers, whichare low-density strand layers 1 b. The two high-density strand layers 1a, 1 a have the same density, which is, e.g., about 1000 kg/m³ (averagevalue). The three low-density strand layers 1 b, 1 b, . . . have thesame density, which is, e.g., about 800 kg/m³. The density of theselow-density strand layers 1 b is about the same as that of common strandboards.

Specifically, the first strand layer 1 located at the top of the strandboard B, the fifth strand layer 1 located at the bottom of the strandboard B, and the third strand layer 1 located in the middle part in thethickness direction of the strand board B are low-density strand layers1 b. Both the second and fourth strand layers 1, 1 located in the partsof the strand board B other than the top and bottom and the middle partin the thickness direction of the strand board B are high-density strandlayers 1 a.

The five strand layers 1, 1, . . . have three different thicknesses. Thethickness of each of the first and fifth strand layers 1, 1 (low-densitystrand layers 1 b) is, e.g., 25% of the total thickness of the strandboard B, the thickness of each of the second and fourth strand layers 1,1 (high-density strand layers 1 a) is, e.g., 20% of the total thicknessof the strand board B, and the thickness of the third strand layer 1(low-density strand layer 1 b) is, e.g., 10% of the total thickness ofthe strand board B. The total thickness of the high-density strandlayers 1 a is therefore, e.g., 40% of the total thickness of the strandboard B. The five strand layers 1, 1, . . . are laminated so thatoverall density distribution provided by the strand layers 1, 1, . . .is plane symmetric with respect to the center in the laminationdirection, namely in the thickness direction, of the strand board B. Thetotal thickness of the strand board B is, e.g., 28 mm.

A method for manufacturing a strand board B according to the secondembodiment will be described. This manufacturing method is applied notonly to the strand board B of the first example but also to the strandboards B of the second to sixth examples.

The manufacturing method of the second embodiment is basically the sameas the first embodiment. Description of the same parts as those in thefirst embodiment is omitted, and only the differences will be describedin detail.

This manufacturing method has a strand producing process, a strandpretreatment process, an adhesive coating process, a stacking process(mat forming process), and a press process. Of these processes, thestrand pretreatment process, the adhesive coating process, and the pressprocess are the same as those of the first embodiment.

In the second embodiment, when forming a multi-layered mat in the matforming process by stacking another strand mat on top of a strand mat,the strand mat that is to be a high-density strand layer 1 a is formedby the strands 5 having a density higher than the strands 5 of thestrand mat that is to be a low-density strand layer 1 b is. This allowsboth high-density and low-density strand layers 1 a, 1 b to be stackedtogether.

For example, the following two kinds of strands are prepared in advancein the first process of the manufacturing method, namely in the strandproducing process: strands with densities in a common range; and strandswith densities higher than the common range. The strands with densitiesin the common range are used as the strands 5 of the strand mat that isto be a low-density strand layer 1 b. The strands with densities higherthan the common range as a result of compression etc. may be used as thestrands 5 of the strand mat that is to be a high-density strand layer 1a.

The wood species etc. of the strands 5 may be different between thestrand mat that is to be a high-density strand layer 1 a and the strandmat that is to be a low-density strand layer 1 b. A wood species havinga higher density may be used to produce the strands 5 of the strand matthat is to be a high-density strand layer 1 a than a wood species thatis used to produce the strands 5 of the strand mat that is to be alow-density layer strand layer 1 b.

After the multi-layered mat is formed, the press process is performed inwhich hot pressing is performed at a predetermined pressure andtemperature with a hot press machine to compress or compact themulti-layered mat. In the press process, the hot pressing is performedat a pressure of, e.g., 2 to 4 N/mm² as in the first embodiment, but thepress time is, e.g., about 10 to 30 minutes. In the second embodiment aswell, the press time varies depending on the thickness of the strandboard B (finished product). Accordingly, in some cases, it may take lessthan 10 minutes to complete the hot pressing, and in other cases, it maytake 30 minutes or more to complete the hot pressing. Pre-heat treatmentwith a heater may be performed before the hot pressing with the hotpress machine.

As described above, it is preferable that the strands 5 produced in thestrand producing process have a density of 300 to 1100 kg/m³ and amoisture content of 2 to 8%. However, the strands 5 produced in thestrand producing process can be used even if their properties are out ofthese preferred ranges.

Second Example

FIG. 4 shows the second example of the strand board B. As in the firstexample, this strand board B has five strand layers, namely first tofifth strand layers 1, 1, . . . . These strand layers 1, 1, . . . arestacked and laminated such that the fibers of the strands 5 in adjoiningones of the strand layers 1 extend in directions perpendicular to eachother. The fiber direction of the strands 5, 5 in the first strand layer1 located at the top of the strand board B, namely in the uppermoststrand layer 1 in FIG. 4, is the same as that of the strands 5, 5 in thefifth strand layer 1 located at the bottom of the strand board B, namelyin the lowermost strand layer 1 in FIG. 4.

Two of the five strand layers 1, 1, . . . are high-density strand layers1 a, and the other three strand layers are low-density strand layers 1 bhaving a density lower than the high-density strand layers 1 a. The twohigh-density strand layers 1 a, 1 a have the same density, which is,e.g., about 1100 kg/m³ (average value). This density is higher than thatof the high-density strand layers 1 a of the first example. The threelow-density strand layers 1 b, 1 b, . . . have the same density, andthis density is lower than that of the low-density strand layers 1 b ofthe first example (because the product density of the strand board B islower than in the first example).

Unlike in the first example, the first strand layer 1 located at the topof the strand board B and the fifth strand layer 1 located at the bottomof the strand board B are high-density strand layers 1 a. The remainingstrand layers, namely the second to fourth strand layers 1, 1, . . .located in the intermediate part in the thickness direction of thestrand board B, are low-density strand layers 1 b.

The five strand layers 1, 1, . . . have the same thickness. Thethickness of each strand layer 1 is, e.g., 20% of the total thickness ofthe strand board B. The total thickness of the high-density strandlayers 1 a is therefore, e.g., 40% of the total thickness of the strandboard B. The five strand layers 1, 1, . . . are laminated so thatoverall density distribution provided by the strand layers 1, 1, . . .is plane symmetric with respect to the center in the thickness directionof the strand board B. The total thickness of the strand board B is,e.g., 9 mm.

Third Example

FIG. 5 shows the third example of the strand board B. Unlike in thesecond example, the strand board B has seven strand layers, namely firstto seven strand layers 1, 1, . . . . These strand layers 1, 1, . . . arestacked and laminated such that the fibers of the strands 5 in adjoiningones of the strand layers 1 extend in directions perpendicular to eachother. The fiber direction of the strands 5, 5 in the first strand layer1 located at the top of the strand board B, namely in the uppermoststrand layer 1 in FIG. 5, is the same as that of the strands 5, 5 in theseventh strand layer 1 located at the bottom of the strand board B,namely in the lowermost strand layer 1 in FIG. 5.

Two of the seven strand layers 1, 1, . . . are high-density strandlayers 1 a. The other five strand layers are low-density strand layers 1b having a density lower than the high-density strand layers 1 a. Thetwo high-density strand layers 1 a, 1 a have the same density, which is,e.g., about 1000 kg/m³ (average value). This density is the same as thatof the high-density strand layers 1 a of the first example. The fivelow-density strand layers 1 b, 1 b, . . . have the same density, andthis density is lower than that of the low-density strand layers 1 b ofthe first example (because the product density of the strand board B islower than in the first example).

Specifically, the first strand layer 1 located at the top of the strandboard B and the seventh strand layer 1 located at the bottom of thestrand board B are high-density strand layers 1 a. The remaining strandlayers, namely the second to sixth strand layers 1, 1, . . . located inthe intermediate part in the thickness direction of the strand board B,are low-density strand layers 1 b.

The seven strand layers 1, 1, . . . have two different thicknesses. Thethickness of each of the first and seventh strand layers 1, 1(high-density strand layers 1 a) is, e.g., 15% of the total thickness ofthe strand board B, the thickness of each of the second, third, fifth,and sixth strand layers 1, 1, . . . (low-density strand layers 1 b) is,e.g., 15% of the total thickness of the strand board B, and thethickness of the fourth strand layer 1 (low-density strand layer 1 b)is, e.g., 10% of the total thickness of the strand board B. The totalthickness of the high-density strand layers 1 a is therefore, e.g., 30%of the total thickness of the strand board B. The seven strand layers 1,1, . . . are laminated so that overall density distribution provided bythe strand layers 1, 1, . . . is plane symmetric with respect to thecenter in the thickness direction of the strand board B. The totalthickness of the strand board B is, e.g., 12 mm.

Fourth Example

FIG. 6 shows the fourth example of the strand board B. Unlike in thesecond and third examples, this strand board B has three strand layers,namely first to third strand layers 1, 1, . . . . These strand layers 1,1, . . . are stacked and laminated such that the fibers of the strands 5in adjoining ones of the strand layers 1 extend in directionsperpendicular to each other. The fiber direction of the strands 5, 5 inthe first strand layer 1 located at the top of the strand board B,namely in the uppermost strand layer 1 in FIG. 6, is the same as that ofthe strands 5, 5 in the third strand layer 1 located at the bottom ofthe strand board B, namely in the lowermost strand layer 1 in FIG. 6.

One of the three strand layers 1, 1, . . . is a high-density strandlayer 1 a. The other two strand layers are low-density strand layers 1 bhaving a density lower than the high-density strand layer 1 a. Thedensity of the high-density strand layer 1 a is, e.g., about 800 kg/m³(average value), which is lower than that of the high-density strandlayers 1 a of the second example. The two low-density strand layers 1 b,1 b, . . . have the same density, and this density is the same as thatof the low-density strand layers 1 b of the first example.

Specifically, only the second strand layer 1 located in the middle part(intermediate part) in the thickness direction of the strand board B isa high-density strand layer 1 a, and the first and third strand layers1, 1 located at the top and bottom of the strand board B are low-densitystrand layers 1 b.

The three strand layers 1, 1, . . . have two different thicknesses. Thethickness of each of the first and third strand layers 1, 1 (low-densitystrand layers 1 b) is, e.g., 20% of the total thickness of the strandboard B, and the thickness of the second strand layer 1 (high-densitystrand layer 1 a) is, e.g., 60% of the total thickness of the strandboard B. The thickness of the high-density strand layer 1 a istherefore, e.g., 60% of the total thickness of the strand board B. Thethree strand layers 1, 1, . . . are laminated so that overall densitydistribution provided by the strand layers 1, 1, . . . is planesymmetric with respect to the center in the thickness direction of thestrand board B. The total thickness of the strand board B is, e.g., 18mm.

Fifth Example

FIG. 7 shows the fifth example of the strand board B. As in the fourthexample, this strand board B has three strand layers, namely first tothird strand layers 1, 1, . . . . Unlike in the first to fourthexamples, these strand layers 1, 1, . . . are stacked and laminated suchthat the fibers of the strands 5 in adjoining ones of the strand layers1 extend in directions parallel to each other. That is, the fiberdirection of the strands 5, 5 in the first strand layer 1 located at thetop of the strand board B, namely in the uppermost strand layer 1 inFIG. 7, is the same as that of the strands 5, 5 in the third strandlayer 1 located at the bottom of the strand board B, namely in thelowermost strand layer 1 in FIG. 7. The fiber direction of the strands5, 5 in the second strand layer 1 located in the middle part in thethickness direction of the strand board B is also the same as that ofthe strands 5, 5 in the first and third strand layers 1.

Unlike in the fourth example, two of the three strand layers 1, 1, . . .are high-density strand layers 1 a. The remaining one strand layer is alow-density strand layer 1 b. The two high-density strand layers 1 a, 1a have a density of, e.g., about 800 kg/m³ (average value). This densityis the same as that of the high-density strand layer 1 a of the fourthexample. The density of the low-density strand layer 1 b is lower thanthat of the low-density strand layers 1 b of the first example (becausethe product density of the strand board B is lower than in the firstexample).

Specifically, the first and third strand layers 1, 1 located at the topand bottom of the strand board B are high-density strand layers 1 a, andonly the second strand layer 1 located in the middle part in thethickness direction of the strand board B is a low-density strand layer1 b.

The three strand layers 1, 1, . . . have two different thicknesses. Thethickness of each of the first and third strand layers 1, 1(high-density strand layers 1 a) is, e.g., 40% of the total thickness ofthe strand board B, and the thickness of the second strand layer 1(low-density strand layer 1 b) is, e.g., 20% of the total thickness ofthe strand board B. The total thickness of the high-density strandlayers 1 a is therefore, e.g., 80% of the total thickness of the strandboard B. The three strand layers 1, 1, . . . are laminated so thatoverall density distribution provided by the strand layers 1, 1, . . .is plane symmetric with respect to the center in the thickness directionof the strand board B. The total thickness of the strand board B is,e.g., 15 mm.

Sixth Example

FIG. 8 shows the sixth example of the strand board B. As in the firstexample, this strand board B has five strand layers, namely first tofifth strand layers 1, 1, . . . . These strand layers 1, 1, . . . arestacked and laminated such that the fibers of the strands 5 in adjoiningones of the strand layers 1 extend in directions perpendicular to eachother. The fiber direction of the strands 5, 5 in the first strand layer1 located at the top of the strand board B, namely in the uppermoststrand layer 1 in FIG. 8, is the same as that of the strands 5, 5 in thefifth strand layer 1 located at the bottom of the strand board B, namelyin the lowermost strand layer 1 in FIG. 8.

Three of the five strand layers 1, 1, . . . are high-density strandlayers 1 a. The other two strand layers are low-density strand layers 1b having a density lower than the high-density strand layers 1 a. Thethree high-density strand layers 1 a, 1 a, . . . have the same density,which is, e.g., about 1000 kg/m³ (average value). This density is thesame as that of the high-density strand layers 1 a of the first example.The two low-density strand layers 1 b, 1 b, . . . have the same density.This density is the same as that of the low-density strand layers 1 b ofthe first example.

Specifically, as opposed to the second example, the second to fourthstrand layers 1, 1, . . . located in the intermediate part in thethickness direction of the strand board B are high-density strand layers1 a. The remaining strand layers, namely the first strand layer 1located at the top of the strand board B and the fifth strand layer 1located at the bottom of the strand board B, are low-density strandlayers 1 b.

The five strand layers 1, 1, . . . have three different thicknesses. Thethickness of each of the first and fifth strand layers 1, 1 (low-densitystrand layers 1 b) is, e.g., 30% of the total thickness of the strandboard B, the thickness of each of the second and fourth strand layers 1,1 (high-density strand layers 1 a) is, e.g., 15% of the total thicknessof the strand board B, and the thickness of the third strand layer 1(high-density strand layer 1 a) is, e.g., 10% of the total thickness ofthe strand board B. The total thickness of the high-density strandlayers 1 a is therefore, e.g., 60% of the total thickness of the strandboard B. The five strand layers 1, 1, . . . are laminated so thatoverall density distribution provided by the strand layers 1, 1, . . .is plane symmetric with respect to the center in the thickness directionof the strand board B. The total thickness of the strand board B is,e.g., 28 mm.

FIG. 9 shows specific configurations of the first to sixth examples.

In the second embodiment, the strand board B has multiple strand layers1, 1, . . . , and a part (one to three) of the multiple strand layers 1,1, . . . is a high-density strand layer 1 a having a density higher thanthe other strand layers 1, 1, . . . . The high-density strand layer 1 aprovides high strength and high water resistance of the strand board B,whereby the strand board B having high strength and high waterresistance is obtained.

In the case where the density of the strand layer 1 is increased to usethis strand layer 1 as a high-density strange layer 1 a in the strandboard B, the density of only the strands 5 of this high-density strandlayer 1 a need be increased, and it is not necessary to increase thedensity of the strands 5 of all the strand layers 1, 1, . . . . Thepress time with a press machine is therefore reduced accordingly and thepressure to be used is also reduced. This improves productivity andreduces or eliminates the risk of delamination in the press process.

Moreover, one to three of the odd number of strand layers 1, 1, . . . ofthe strand board B are high-density strand layers 1 a. Accordingly, asshown in the first to sixth examples, a layer(s) to be used as ahigh-density strand layer(s) 1 a can be selected from the multiplestrand layers 1, 1, . . . as necessary. Characteristics of the strandboard B can therefore be varied as desired by changing the position(s)of the high-density strand layer(s) 1 a, so that the strand board B hasadvantageous effects specific to each example.

That is, in, e.g., the first example shown in FIGS. 2 and 3 (the sixthexample shown in FIG. 8 is substantially similar to this configuration),the second and fourth strand layers 1, 1 located in the parts of thestrand board B other than the top and bottom and the middle part in thethickness direction of the strand board B are high-density strand layers1 a, and the remaining layers, namely the first, third, and fifth strandlayers 1, 1, . . . located at the top and bottom and in the middle partin the thickness direction of the strand board B, are low-density strandlayers 1 b. This structure is advantageous in that the use of thelow-density strand layers 1 b in the top and bottom parts reduces thepressure to be used in the press process and the high-density strandlayers 1 a provide increased nail pull resistance (force) for a nailthat is a fastener to be driven into the strand board B. Especially, thesixth example shown in FIG. 8 further improves productivity.

In the second example shown in FIG. 4 and the third example shown inFIG. 5, the strand layers 1, 1 located at the top and bottom of thestrand board B are high-density strand layers 1 a, and the strand layers1, 1, . . . located in the intermediate part of the strand board B arelow-density strand layers 1 b. In this structure, the high-densitystrand layers 1 a in the top and bottom parts increase flexural strengthof the strand board B and improve water resistance in the top and bottomparts of the strand board B.

In the fourth example shown in FIG. 6, the strand layer 1 located in theintermediate part in the thickness direction of the strand board B is ahigh-density strand layer 1 a, and the strand layers 1, 1 located in theremaining part of the strand board B are low-density strand layers 1 b.In this structure, the strand board B has a higher density in itsintermediate part due to the high-density strand layer 1 a, and thestrand board B has uniform overall density distribution in the thicknessdirection. Since the high-density strand layer 1 a is formed in theintermediate part in the thickness direction of the strand board B andthe low-density strand layers 1 b are formed in the top and bottom partsof the strand board B, this structure effectively reduces or eliminatesthe risk of delamination in the press process and improves productivity.

In the fifth example shown in FIG. 7, the strand layer 1 located in themiddle part in the thickness direction of the strand board B is ahigh-density strand layer 1 a, and the first and third strand layers 1,1 located at the top and bottom of the strand board B are low-densitystrand layers 1 b. Moreover, the fiber direction of the strands 5, 5, .. . is the same in all of the first to third strand layers 1, 1 . . . .This structure improves flexural strength in the fiber direction andalso improves shear strength.

In the first to fourth examples of the strand board B of the secondembodiment, the fibers of the strands 5, 5, . . . extend in the samedirection in each strand layer 1, and the fibers of the strands 5 inadjoining ones of the strand layers 1 extend in directions perpendicularto each other. This structure has high strength against forces acting invarious directions as compared to the case where the fibers of thestrands 5 extend in the same direction in all of the strand layers 1, 1,. . . as in the fifth example. The larger the number of strand layers 1is, the more significant the difference in strength of the strand boardB due to the difference in fiber direction between the strand layers 1is.

On the other hand, in the case where the strands 5, 5 are oriented inthe same direction along the entire thickness in the laminationdirection of the strand board B as in the fifth example, the strandboard B has high strength against a force acting in a specificdirection, as described above.

In the second embodiment as well, density distribution in the thicknessdirection of the strand board B formed by the strand layers 1, 1, . . .is plane symmetric. This allows the strand board B to have similarperformance in its top and bottom parts. The user can therefore use thestrand board B without having to know which side is the top and whichside is the bottom.

Moreover, the strand board B has an odd number of strand layers 1, 1, .. . . This allows the strand board B to have similar performance in itstop and bottom parts.

OTHER EMBODIMENTS

The present invention is not limited to the first and secondembodiments. In the first embodiment, the thicknesses w1 to w3 of themultiple strand layer 1, 1, . . . are the same. However, the presentinvention is not limited to this, and the thicknesses W1 to W3 of eachlayer 1 can be set as desired.

For example, the multiple strand layers 1, 1, . . . may be composed sothat the thickness of the strand layer 1 gradually increases from themiddle strand layer 1 in the thickness direction (lamination direction)of the strand board B to the top and bottom strand layers 1. That is,the thicknesses of the multiple strand layers 1, 1, . . . in FIG. 1 mayhave a relation of w1>w2>w3. The strand layers 1 on the outer sides (topand bottom) of the strand board B, which are more likely to be subjectedto load and impact and are more susceptible to humidity etc., have alarger thickness than the remaining strand layer(s) 1. This allows thestrand board B to have improved performance regarding influences fromthe external environment.

One or more of the strand layers 1, 1, . . . may have a differentthickness from the remaining strand layer(s) 1. For example, thethickness w1 of the top and bottom strand layers 1, 1 may be differentfrom the thicknesses w2, w3 of the three intermediate strand layers 1,1, . . . . Although not shown in the figures, all of the five strandlayers 1, 1, . . . may have different thicknesses from each other.

In the first embodiment, the fiber direction of the strands 5, 5, . . .in every strand layer 1 is perpendicular to that of the strands 5, 5, .. . in its adjoining strand layer 1. However, the present invention isnot limited to this. For example, the fiber direction of the strands 1,1, . . . in a part of the multiple strand layers 1, 1, . . . may be thesame as that of the strands 5, 5, . . . in its adjoining layer 1. Forexample, in the case where the strand layers 1, 1 that are different inform of the strands 5, 5, . . . such as length or density of the strands5, 5, . . . from each other are formed so as to adjoin each other, thefiber directions of the strands 5, 5, . . . in these adjoining strandlayers 1, 1 may be the same.

In the first embodiment, the density or thickness of the strands 5(woodbased materials) may be different between or among the strandlayers 1, 1, . . . of the strand board B.

For example, in the stacking process (mat forming process), the multiplemats of strands 5, 5, . . . may be stacked so that the relative densityof the strands 5 of the mat gradually increases from the top and bottomstrand layers 1 to the middle strand layer 1 in the thickness directionof the strand board B. When the multi-layered mat is pressed in thepress process, the relative density of the outer strand layers 1 thatare directly subjected to the pressure of a press machine typicallytends to become higher than that of the inner strand layer(s) 1. Sincethe relative density of the strands 5 of the inner strand layer(s) 1 isthus made higher than that of the strands 5 of the outer strand layers 1prior to the pressing, the strand board B formed by the pressing hasuniform density distribution in the lamination direction. In this case,the wood species of the strands 5 may be different or the same betweenor among the strand layers 1.

That is, in a part of the strand layers 1 or all of the strand layers 1,the wood species, thickness, density, etc. of the strands 5 of thestrand layer 1 can be selected as appropriate according to requiredcharacteristics, cost, etc.

In the stacking process (mat forming process) of the first embodiment,the strand mats may be stacked so that at least one of the multiplestrand layers 1, 1, . . . is formed by the strands 5, 5, . . . with ahigh density. This strand layer 1 is a layer formed by the strands 5having a relatively higher density than the other strand layers 1.Specifically, in the case where the strand board B has, e.g., an oddnumber of strand layers 1, the strand mats may be stacked so that anodd-numbered strand layer 1 from the top or bottom of the strand board Bis formed by the high-density strands 5. The strand mats may be stackedso that a specific one (at least one) of the multiple strand layers 1,1, . . . are formed by the high-density strands 5, 5, . . . accordingto, e.g., the use of the strand board B, required strength propertiesand other performance of the strand board B, etc. In the case wherethere are multiple strand layers 1 that are formed by the high-densitystrands 5, 5, . . . , these strand layers 1, 1, . . . may be differentin density and thickness from each other.

In the second embodiment, the strand board B has an odd number of strandlayers 1, 1, . . . . However, the strand board B may have an even numberof strand layers 1. It is preferable that the strand board B have an oddnumber of strand layers 1, 1, . . . because this allows the strand boardB to have similar performance in its top and bottom parts.

In the second embodiment, the fibers of the strands 5 extend in the samedirection in each strand layers 1, and the fiber directions of thestrands 5, 5 of adjoining ones of the strand layers 1 are eitherperpendicular or parallel to each other. However, the present inventionis not limited to this. The fiber direction of the strands 5 of eachstrand layer 1 may be determined as desired.

The first and second embodiments are described with respect to thestrand board B formed by stacking and laminating the mats of the strands5 into the shape of a board. However, the present invention is notlimited to this strand board B. For example, multiple strand layershaving a rectangular section (in the shape of squared timber) and havingno significant difference between their thickness and width may bestacked and laminated. In this case, a strand material (wood laminatematerial) can be used as a joist, pillar, etc. formed by stacking andlaminating multiple strand layers.

The first and second embodiments are examples of the strand board Bformed by stacking and laminating the multiple strand layers 1, 1, . . .each formed by laminated multiple strands 5, 5, . . . . However, thepresent invention is also applicable to, e.g., plywood and laminatedveneer lumber (LVL). Specifically, veneers may be used instead of themats of strands 5. That is, in the case of plywood and LVL, eachwoodbased material layer is formed by at least one veneer.

In the case where the wood laminate material is plywood or LVL, a commonmanufacturing method is used to manufacture plywood or LVL.Specifically, green wood such as logs or thinnings is cut with a cuttingmachine to produce veneers. Multiple veneers are then stacked togetherwith an adhesive therebetween such that the fiber directions ofadjoining ones of the veneers are the same in the case of LVL and thefiber directions of adjoining ones of the veneers are perpendicular toeach other in the case of plywood. Subsequently, the staked veneers areformed by cold pressing or hot pressing to cure the adhesive.

In the case where density distribution in the lamination direction ofthe woodbased material layers is to be made substantially uniform as inthe first embodiment, the density, thickness, etc. of each veneer areadjusted before, e.g., the stacked veneers are formed in the pressprocess.

In the case where the woodbased material layers consist of a combinationof high-density and low-density woodbased material layers as in thesecond embodiment, the density of the woodbased material or woodbasedmaterials forming each woodbased material layer is made higher in a partof the woodbased material layers than in the remainder of the woodbasedmaterial layers by wood species etc. before, e.g., the stacked veneersare formed in the press process.

EXAMPLES

Next, specific examples of the strand boards according to the first andsecond embodiments will be described. It should be noted that “examples”and “comparative examples” of the first embodiment are different from“examples” and “comparative examples” of second embodiments even thoughtheir numbers are the same. The examples and the comparative examplesare specified for each embodiment.

First Embodiment Example 1

Mats of a large number of cypress strands were stacked into amulti-layered mat having five strand layers and a thickness of 37 mm.The strands were 150 to 200 mm long in the fiber direction, 15 to 25 mmwide, and 0.8 to 2 mm thick and had a density of 500 to 600 kg/m³. Themulti-layered mat was then subjected to hot pressing at 140° C. and 4N/mm² for 10 minutes, whereby a strand board with a density of 818 kg/m³and a thickness of 12.4 mm was obtained. This strand board was used asExample 1.

FIG. 10 shows an image of Example 1. In FIG. 10, reference character “B”indicates the strand board and “1” indicates the strand layers. FIG. 11shows the results of a bending test, a dimensional change test, and awater absorption test for Example 1. FIG. 12 shows the densitydistribution in the thickness direction (lamination direction) of thestrand board measured with a density profile analyzer (“DENSE-LAB X”made by ELECTRONIC WOOD SYSTEMS GMBH).

Example 2

Mats of a large number of Douglas fir strands were stacked into amulti-layered mat having five strand layers and a thickness of 36 mm.The strands were 150 to 200 mm long in the fiber direction, 15 to 25 mmwide, and 0.8 to 2 mm thick and had a density of 450 to 550 kg/m³. Themulti-layered mat was then subjected to hot pressing at 140° C. and 4N/mm² for 10 minutes, whereby a strand board with a density of 832 kg/m³and a thickness of 12.2 mm was obtained. This strand board was used asExample 2. FIG. 11 shows the results of the bending test, thedimensional change test, and the water absorption test for Example 2.

Comparative Example 1

Mats of a large number of cypress strands were stacked into amulti-layered mat having five strand layers and a thickness of 42 mm.The strands were 150 to 200 mm long in the fiber direction, 15 to 25 mmwide, and 0.8 to 2 mm thick and had a density of 400 to 500 kg/m³. Themulti-layered mat was then subjected to hot pressing at 140° C. and 8N/mm² for 10 minutes, whereby a strand board with a density of 779 kg/m³and a thickness of 12.7 mm was obtained. This strand board was used asComparative Example 1. FIG. 11 shows the results of the bending test,the dimensional change test, and the water absorption test forComparative Example 1. FIG. 13 shows the density distribution in thethickness direction (lamination direction) of the strand board measuredwith the density profile analyzer (“DENSE-LAB X” made by ELECTRONIC WOODSYSTEMS GMBH).

Comparative Example 2

Mats of a large number of Douglas fir strands were stacked into amulti-layered mat having five strand layers and a thickness of 35 mm.The strands were 150 to 200 mm long in the fiber direction, 15 to 25 mmwide, and 0.8 to 2 mm thick and had a density of 350 to 450 kg/m³. Themulti-layered mat was then subjected to hot pressing at 140° C. and 8N/mm² for 10 minutes, whereby a strand board with a density of 812 kg/m³and a thickness of 12.4 mm was obtained. This strand board was used asComparative Example 2. FIG. 11 shows the results of the bending test,the dimensional change test, and the water absorption test forComparative Example 2.

The results in FIG. 11 show that Example 1 is higher in density,flexural strength, modulus of rupture (MOR), and modulus of elasticity(MOE) than Comparative Example 1. Percentage dimensional change andwater absorption of Example 1 are about the same as those of ComparativeExample 1. Example 2 has a higher density than Comparative Example 2,approximately the same flexural strength and MOR as Comparative Example2, and a higher MOE than Comparative Example 2. Percentage dimensionalchange and water absorption of Example 2 are about the same as those ofComparative Example 2.

The results in FIGS. 12 and 13 show that Example 1 has substantiallyconstant density distribution in the lamination direction of themultiple strand layers as compared to Comparative Example 1. Thesubstantially constant density distribution includes such densitydistribution that, in the case where the measurement result of thedensity distribution varies as shown in, e.g., FIGS. 12 and 13, themedian shown by dashed line as shown in each figure does not varysignificantly but is substantially constant. For example, as can be seenfrom comparison between the dashed line shown in FIG. 12 (Example 1) andthe dashed line shown in FIG. 13 (Comparative Example 1), the median ofthe density distribution shown in FIG. 12 varies less than the median ofthe density distribution shown in FIG. 13, and the median of the densitydistribution shown in FIG. 12 is substantially constant.

Since the density distribution is substantially constant, the strandboard has uniform density distribution and overall water resistance andstrength (shear strength etc.) of the strand board are improved.Specifically, a portion with a low density has lower water resistanceand strength than a portion with a high density. Accordingly, if thedensity distribution is uneven, the overall performance of the strandboard is governed by the water resistance and strength of the portionwith a low density. However, in the case where the density distributionis substantially constant, such a portion that becomes a bottleneck forperformance can be eliminated.

The above bending test was conducted in accordance withIICL_Floor_Performance TB001 Ver. 2. The dimensional change test and thewater absorption test were conducted in accordance with the cyclicboiling test of Japanese Agricultural Standard for plywood.

Second Embodiment Example 1

Mats of a large number of aspen strands were stacked into amulti-layered mat having five strand layers and a thickness of 53 mm.The strands had a thickness of 0.8 mm and a density of 300 to 600 kg/m³.As in the second example (see FIG. 4) of the strand board of the secondembodiment, strands with common densities (average value: 393 kg/m³)were used for the second to fourth strand layers located in theintermediate part in the lamination direction out of the five strandlayers. Strands with higher densities (average value: 557 kg/m³) thanthe common densities were used for the first and fifth strand layerslocated at both ends in the lamination direction.

The multi-layered mat was then subjected to hot pressing at 160° C. and4 N/mm² for 8 minutes. The strand board thus obtained was used asExample 1. The time required to achieve a target thickness, namely thetime required to press the multi-layered mat to a target thickness, was24 seconds.

Example 2

A multi-layered mat having five strand layers and a thickness of 52 mmwas formed in a manner similar to that in Example 1. Strands having adensity (average value: 805 kg/m³) higher than Example 1 were used forthe first and fifth strand layers located at both ends in the laminationdirection out of the five strand layers. The multi-layered mat was thensubjected to hot pressing under conditions similar to those inExample 1. The strand board thus obtained was used as Example 2. Thetime required to achieve a target thickness was 12 seconds. Example 2 isotherwise the same as Example 1.

Comparative Example 1

A multi-layered mat having five strand layers and a thickness of 62 mmwas formed in a manner similar to that in Example 1. Strands with commondensities (average value: 393 kg/m³) were used for all of the fivestrand layers. The multi-layered mat was then subjected to hot pressingunder conditions similar to those in Example 1. The strand board thusobtained was used as Comparative Example 1. The time required to achievea target thickness was 33 seconds. Comparative Example 1 is otherwisethe same as Example 1.

(Test A)

A normal-state bending test (bending test span: 225 mm) was conducted oneach of Examples 1, 2 and Comparative Example 1. FIG. 14 shows the testresults along with other physical properties.

Density distribution in thickness direction (lamination direction) ofeach strand board was measured with the density profile analyzer(“DENSE-LAB X” made by ELECTRONIC WOOD SYSTEMS GMBH). FIG. 15 shows themeasurement results.

The results in FIG. 14 show that, as can be seen from comparison betweenExamples 1, 2 and Comparative Example 1, the use of high-density strandlayers as the first and fifth strand layers located at the top andbottom out of the five strand layers allows the multi-layered mat beforehot pressing to have a smaller thickness (bulk height) and thusfacilitates compression of the multi-layered mat by hot pressing,thereby reducing the press time required to press the multi-layered matto a target thickness (time to achieve the target thickness). Regardingflexural properties in the normal-state bending test, MORs and MOEs ofExamples 1, 2 are about the same as those of Comparative Example 1.

Example 3

Mats of a large number of aspen strands were stacked into amulti-layered mat having five strand layers and a thickness of 70 mm.The strands had a thickness of 0.8 mm and a density of 300 to 600 kg/m³.As in the first example (see FIG. 3) of the strand board of the secondembodiment, strands with common densities (average value: 393 kg/m³)were used for the first, third, and fifth strand layers of the fivestrand layers, namely the strand layers other than the second and fourthstrand layers located in the intermediate part in the laminationdirection. Strands with higher densities (average value: 933 kg/m³) thanthe common densities were used for the second and fourth strand layers.

The multi-layered mat was then subjected to hot pressing at 140° C. and4 N/mm² for 10 minutes, whereby a strand board having a density of 846kg/m³ and a thickness of 12.5 mm was obtained. This strand board wasused as Example 3. The MDI content or dozing was 12%.

Comparative Example 2

A multi-layered mat having five strand layers and a thickness of 78 mmwas formed in a manner similar to that in Example 3. Strands with commondensities (average value: 393 kg/m³) were used for all of the fivestrand layers. The multi-layered mat was then subjected to hot pressingat 140° C. and 8 N/mm² for 10 minutes, whereby a strand board having adensity of 846 kg/m³ and a thickness of 12.6 mm was obtained. Thisstrand board was used as Comparative Example 2. Comparative Example 2 isotherwise the same as Example 3.

(Test B)

A normal-state bending test and a boiling test were conducted on Example3 and Comparative Example 2. The boiling test was conducted inaccordance with the cyclic boiling test defined in Japanese AgriculturalStandard for Plywood. After the boiling test was conducted twice,thickness swelling TS, water absorption WA, and internal bond strengthIB were measured. FIG. 14 shows the measurement results along with otherphysical properties.

FIG. 17 shows density distribution in the thickness direction(lamination direction) of each strand board measured with the densityprofile analyzer as in Test A.

The results in FIG. 16 show that, regarding Example 3 in which thesecond and fourth strand layers located in the intermediate part in thethickness direction out of the five strand layers are high-densitystrand layers and Comparative Example 2 in which all of the five strandlayers are low-density strand layers, flexural strength and internalbond strength IB after the boiling tests of Example 3 are either thesame or higher than Comparative Example 2. Namely, the flexural strengthand internal bond strength IB after the boiling tests of Example 3 arenot lower than Comparative Example 2.

The results thus show that the use of high-density strand layers as thesecond and fourth strand layers of the five strand layers allows astrand board with performance similar to that of Comparative Example 2to be formed by using a lower pressure of 4 N/mm² instead of such a highpressure (8 N/mm²) as used in Comparative Example 2.

Example 4

Mats of a large number of aspen strands were stacked into amulti-layered mat having five strand layers and a thickness of 130 mm.The strands had a thickness of 0.8 mm and a density of 300 to 600 kg/m³.As in the sixth example (see FIG. 8) of the strand board of the secondembodiment, strands with common densities (average value: 413 kg/m³)were used for the first and fifth strand layers of the five strandlayers, namely for the strand layers other than the second to fourthstrand layers located in the intermediate part in the laminationdirection. Strands with higher densities (average value: 1100 kg/m³)than the common densities were used for the second to fourth strandlayers.

The multi-layered mat was then subjected to hot pressing at 160° C. and8 N/mm² for 60 minutes, whereby a strand board having a predetermineddensity and thickness (see FIG. 18) was obtained. This strand board wasused as Example 4.

Comparative Example 3

A multi-layered mat having five strand layers was formed in a mannersimilar to that in Example 4. Strands with common densities (averagevalue: 413 kg/m³) were used for all of the five strand layers. Themulti-layered mat was then subjected to hot pressing at 140° C. and 8N/mm² for 60 minutes, whereby a strand board having a predetermineddensity and thickness (see FIG. 18) was obtained. This strand board wasused as Comparative Example 3. The processes were otherwise the same asthose of Example 4.

Comparative Example 4

A multi-layered mat having five strand layers was formed in a mannersimilar to that in Example 4. Strands with common densities (averagevalue: 413 kg/m³) were used for all of the five strand layers. Themulti-layered mat was then subjected to hot pressing at 160° C. and 8N/mm² for 30 minutes, whereby a strand board having a predetermineddensity and thickness was obtained. This strand board was used asComparative Example 4. In Comparative Example 4, hot pressing wasperformed at a higher temperature than in Comparative Example 3 in orderto avoid insufficient curing of an adhesive during winter time.Comparative Example 4 is small in size, and the press time was shorterthan in Example 4 and Comparative Example 3. The processes wereotherwise the same as those of Example 4.

(Test C)

A normal-state bending test, a boiling test, and a bond durability testwere conducted on Example 4 and Comparative Example 3. FIG. 18 shows thetest results along with other physical properties. In FIG. 18, “ElasticLimit Pmax” refers to elastic limit load, “Ratio of ELP” refers to theratio of Elastic Limit Pmax to maximum load (Pmax), and “Inside ShareStrength” refers to internal shear fracture strength. Regarding thebending direction, “longitudinal” refers to the longitudinal directionof the board, “lateral” refers to the lateral direction of the board,and “N=2 (N=3)” means that the number of test pieces was 2 or 3.Moreover, “TS” indicates thickness swelling, “WA” indicates waterabsorption, and “IB” indicates internal bond strength.

A nail pull test was conducted on Example 4 and Comparative Example 4.In the nail pull test, a lead hole with an inside diameter of 2 mm and adepth of 25 mm was formed in advance in each sample of Example 4 andComparative Example 4. Three samples of Example 4 and four samples ofComparative Example 4 were tested, and the average value of the sampleswas calculated for each of Example 4 and Comparative Example 4. FIG. 19shows the results.

FIG. 20 shows density distribution in the thickness direction(lamination direction) of each strand board measured with the densityprofile analyzer as in Test A.

The results in FIG. 18 show that, regarding Example 4 in which thesecond to fourth strand layers located in the intermediate part in thelamination direction out of the five strand layers are high-densitystrand layers and Comparative Example 3 in which all of the five strandlayers are low-density strand layers, flexural strength of Example 4 isabout the same as that of Comparative Example 3, and internal bondstrength after the boiling test of Example 4 is higher than that ofComparative Example 3.

These results show that the use of high-density strand layers as thesecond to fourth strand layers of the five strand layers allows a strandboard with performance similar to that of Comparative Example 3 to beformed.

The results of FIG. 19 show that the use of high-density strand layersas the second to fourth strand layers located in the intermediate partin the thickness direction out of the five strand layers increases nailpull resistance (force) and achieves improvement in performance.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use as flooring materials forcontainers, watercraft, vehicles, etc. The present invention isextremely useful as new building materials that are suitable for use asflooring materials and structural bracing boards for buildings such ashouses. The present invention thus has high industrial applicability.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   B Strand Board (Wood Laminate Material)    -   1 Strand Layer (Woodbased Material Layer)    -   1 a High-Density Strand Layer (High-Density Woodbased Material        Layer)    -   1 b Low-Density Strand Layer (Low-Density Woodbased Material        Layer)    -   5 Strand (Cut Piece)

1-4. (canceled)
 5. A wood laminate material formed by stacking andlaminating multiple woodbased material layers each formed by laminatedwoodbased materials that are laminated multiple cut pieces or awoodbased material that is a veneer, wherein the multiple woodbasedmaterial layers include at least one high-density woodbased materiallayer, the remainder of the multiple woodbased material layers is alow-density woodbased material layer, and the high-density woodbasedmaterial layer has a higher density than the low-density woodbasedmaterial layer, and the woodbased material layers located at both endsin the lamination direction of the woodbased material layers are thehigh-density woodbased material layers.
 6. (canceled)
 7. A wood laminatematerial formed by stacking and laminating multiple woodbased materiallayers each formed by laminated woodbased materials that are laminatedmultiple cut pieces or a woodbased material that is a veneer, whereinthe multiple woodbased material layers include at least one high-densitywoodbased material layer, the remainder of the multiple woodbasedmaterial layers is a low-density woodbased material layer, and thehigh-density woodbased material layer has a higher density than thelow-density woodbased material layer, and the woodbased material layerlocated in a part other than the ends and a middle part in thelamination direction of the woodbased material layers is thehigh-density woodbased material layer. 8-12. (canceled)
 13. A method formanufacturing a wood laminate material, comprising: a stacking step ofstacking multiple woodbased materials, which are cut pieces or veneers,to form multiple woodbased material layers so that at least one of themultiple woodbased material layers is formed by a high-density woodbasedmaterial or high-density woodbased materials having a relatively higherdensity than the remainder of the woodbased material layers; and aforming step of compressing or compacting the multiple woodbasedmaterial layers formed in the stacking step.